The present invention relates to a device for switching a combustion engine from a propelling mode to a braking mode wherein the combustion engine has at least one intake valve and at least one exhaust valve for each cylinder. The intake valve is actuated by an intake cam and the exhaust valve is actuated by an exhaust cam connected to a cam shaft with the interposition of a hydraulic linkage between the cam shaft and the push rods of the valves. The hydraulic linkage has transmitting and receiving pistons and is connected to a control device.
From German Offenlegungsschrift 30 26 529 it is known to interpose a hydraulic linkage between a cam shaft and the push rod for actuating an exhaust valve. The cam shaft is provided with an exhaust cam which initially activates a push rod that functions as a cylinder. The push rod is provided with a receiving piston in its interior which transmits its movement to the push rod and which, via a rocker arm, actuates the exhaust valve. For activating the receiving piston during braking operation a control bore is provided which is in contact with an external control device. The control device is in the form of a multi-cylinder pump which upon actuation of the motor brake loads the transmitting piston with hydraulic oil and thus opens the exhaust valve during the compression stroke. Such a device requires a great constructive expenditure with respect to the pump. Between pump and receiving piston a relatively long pressure line is required which unfavorably effects the control times due to the travel time of the pressure wave from the pump to the receiving piston.
Based on a motor brake of the aforementioned kind, it is an object of the present invention to provide a device for switching from one operating mode to another operating mode, for example, from a four-stroke engine operation to a two-stroke braking operation.